This invention is directed to a silicone emulsion containing only certain nonionic surfactants. It has been found that such emulsions possess unexpected properties when applied in the field of personal care.
An emulsion is a disperse system consisting of two or more mutually insoluble or sparingly soluble liquids. One liquid is termed the continuous or external phase in which a second liquid is dispersed in the form of particles. The second liquid is termed the internal or dispersed phase. Emulsions are prepared by mechanically breaking up the internal phase. Typically, high-speed stirrers, propeller or turbine agitators, colloid mills, and homogenizers are employed. Emulsifiers or surfactants prevent droplets from reuniting once they are formed, and if the external phase consists of water and the internal phase is an organic liquid, an oil-in-water emulsion is produced. If water is finely dispersed in a nonaqueous liquid, the result is a water-in-oil emulsion.
In the majority of cases, emulsions are prepared with the aid of one or more emulsifiers each having a different HLB value. There are four categories of surface active emulsifiers namely nonionic, anionic, cationic, and ampholytic or amphoteric. In anionic surfactants, the surface active ion carries a negative charge. In cationic surfactants, the charge is positive. In nonionic surfactants, there is no charge on the molecule. In ampholytic and amphoteric surfactants, both positive and negative charges exist in the molecule.
In order to assist formulators in the selection of an emulsifier or surfactant system, a dimensionless number between 1-20 has been assigned to each emulsifier for the purpose of providing information on its water and oil solubility. Numbers between 0-9 characterize oil soluble lipophilic products, whereas numbers between 11-20 indicate water soluble hydrophilic compounds. Substances with a hydrophilic-lipophilic balance (HLB) value of 10 have about the same affinity for both oil and water, and are distributed between the two phases so that the hydrophilic group projects completely into the water while the lipophilic hydrocarbon group is adsorbed in the nonaqueous phase. Surfactants with an HLB value of eleven or more are known to stabilize emulsions against particle coalescence.
The color of an emulsion often reveals a rough indication of the particle size of the droplets in the internal phase. If the particles are macroglobules, two phases may be distinguished. If the particle size exceeds one micron, milky-white emulsions are formed. If the particle size falls within the range of 0.1-1.0 microns, emulsions exhibiting a blue-white hue are produced. Emulsions containing particles with a size in the range of 0.05-0.1 microns possess a gray semitransparent appearance. Transparent emulsions result where the particle size is 0.05 microns and less.
The contribution to the existing state of the emulsion art provided in accordance with the present invention resides in the unexpected discovery that the level of resistance of water penetration through a silicone oil residue deposited from an oil-in-water emulsion into a substrate may be increased by forming the oil-in-water silicone emulsion with the aid of two specific and particular types of nonionic surfactant. More particularly, there must be employed at least one nonionic surfactant having a lower HLB value less than 8.0, and preferably a nonionic surfactant which is a solid at room temperature having an HLB value less than 6.0. It is also possible to employ a fatty alcohol such as lauryl alcohol, myristyl alcohol, stearyl alcohol, behenyl alcohol, or cetyl alcohol, as the lower HLB value surfactant. The lower HLB value surfactant is used in combination with at least one nonionic surfactant having a higher HLB value greater than 15.0, and preferably a nonionic surfactant which is a solid at room temperature and which has an HLB value greater than 17.0. Excluded and otherwise considered to be inoperative nonionic surfactants in accordance with the concept of the present invention are liquid nonionic surfactants, and nonionic surfactants having a range of HLB values of 8.0-15.0.
The advantages provided by the present invention are realized by complying with the foregoing requirements of the surfactant package. Other anionic, cationic, ampholytic, or amphoteric surface active emulsifiers may be present in smaller amounts of less than about one percent by weight in those situations wherein the emulsion is prepared by emulsion polymerization in which an ionic surfactant is required as a constituent of the polymerization catalyst.